Yes, but really close. I think it's awkward to start with "I began to worry" because there's no frame of reference for me. But I like the idea! I think it might be better to play it bold: My reflection had stopped looking me in the eye.

Yes. That would worry me, too! Actually, I don't love "I began to worry," as a starting point, but the visual that I get of my own eyes shifting from contact in the mirror is strong enough to engage me.

No. I want to, but no. "I began to worry" sounds to casual for the occasion, and I think "when my reflection stopped looking me in the eye," would be much stronger as "when my reflection looked away." I guess it's much creepier to me to think of my reflection doing something it isn't supposed to do than not doing something it is, if that makes sense. I like the idea, but I don't think your writing adequately conveys the terror of the moment.

Yes. The narrator has stopped looking herself in the eye and I wonder why. I'm also intrigued because this is designated as fiction rather than scifi or fantasy. To me that means this person has something she really doesn't want to face and I wonder what it is.

Yes. I mean I'd be worried too. I need to know more. I do see Barbara's point but just changing it to "I worried when my reflection stopped looking back at me." would keep your structure and punch up the sentence. - But I read on either way.